P0300 code on 2004 GMC Yukon XL Denali - 119,000 miles

[zaahirkhan49]

2004 GMC Yukon XL Denali - 119,000 miles

Have had a P0300 code for a while now. Changed everything from spark plugs to lifters, cleaned as much dirt and carbon off the engine, but I still get the same code. After driving for a while, there is a noticeable shake / vibration at idle. Also, all of my monitors seem ok except for the EVAP system monitor, so I am guessing it must be an EVAP related issue? I have pretty much run out of options at this point and am left with the option of just replacing the entire engine. Is there anything else I could do before going that route? Maybe I have to redo the crankshaft relearn? Also, I do get a faulty knock sensor code too but that goes away so I don’t think the knock sensor is an issue but I will still take another look at it. Any advice would be appreciated. TIA!

 

[Fless]

Definitely do the CASE relearn just to rule it out.

Throttle body been cleaned lately?

What do your short- and long-term fuel trims look like?

 

[zaahirkhan49]

Definitely do the CASE relearn just to rule it out.

Throttle body been cleaned lately?

What do your short- and long-term fuel trims look like?

How do I do the CASE relearn?

Throttle body was cleaned out within the last two weeks, when I replaced the lifters.

I also changed the fuel pump already so i’m guessing the fuel trims are ok. I do not have the proper scan tool to see the fuel trims.

 

[TJ Baker]

I do not have the proper scan tool to see the fuel trims.

Does not require much. I get this (and far more) for under $20 with a Veepeak OBD2 adapter and the Car Scanner ELM OBD app.

 

[S33k3r]

How do I do the CASE relearn?

Throttle body was cleaned out within the last two weeks, when I replaced the lifters.

I also changed the fuel pump already so i’m guessing the fuel trims are ok. I do not have the proper scan tool to see the fuel trims.

I do suggest getting a scan tool. That said, have you looked at your purge valve, charcoal canister, and/or the evap system lines? Since it is an intermittent issue, I'd look at the purge valve first. You might get lucky and just need to clean it.

Good luck in any case. I really hope you get this figured out and become a regular around here. This is one of THE best places on the Internet for car enthusiasts in general, and Tahoes/Yukons/Escalades/etc. in specific. Also, sometimes we are even funny.

 

[Fless]

You would need a bi-directional scanner to run the CASE (correlation) relearn.

The reason I also asked about fuel trims is that some emissions components (among many things) can cause the trims to be out of whack. If they're okay, then that takes us in a slightly different direction.

 

[drdave81]

I had a P0300 that I couldn't figure out at all. Misfire monitors were all over the place. Every ignition cycle showed different cylinders misfiring, fuel trims weren't telling me much either. I ended up running a crank sensor relearn (CASE) and that was enough to get the light off. Basically that will tell you if your timing chain has stretched enough to cause the crank sensor to be reading out of calibrated specs and throwing the code. Ultimately, you'd need a new timing chain at that point, but it's a bandaid.

 

[03yukXL]

As others have said it could be a number of things. Mine ended up being bad intake gaskets, which caused a vacuum leak. Have a look at your fuel trims. Try a can of carb cleaner around the intake mating surface to see if idle increases while running. If it’s bad enough you can find a vacuum leak.